Using 29 years of expendable bathythermograph data, we studied the interann
ual temperature variability in the upper 300 m of the South China Sea (SCS)
. It is found that the temperature field has significant quasi-penta-annual
variability throughout the 29 years. The interannual variability has a lar
ge decadal modulation. Although outside the SCS, in the Kuroshio, significa
nt interannual variability extends to a much deeper layer beyond the 300 m
depth, inside the SCS, especially in the central SCS, strong interannual va
riability is located near the 100 m depth and is capped by a surface layer
of much weaker interannual variability. Similarities and differences in the
temporal characteristics between the interannual variability inside and ou
tside the SCS suggest that the interannual variability inside the SCS is pr
imarily generated locally inside the SCS. In addition to the strong interan
nual variability, there exist strong decadal variability and a linear trend
, which are also stronger in the subsurface than near the surface. It is fo
und that below 100 m, the SCS has been cooling (linear trend) at a rate of
similar to 0.4 degrees C per decade, decreasing from the eastern to the wes
tern basin.